First of all you need to get reliable dedicated webhost who can offer you secure hardware and services, secondly try to install APF firewall on your server to prevent such unauthorise attacks for your server and lastly you should know how to ban specific IP from accessing your server. This can be somewhat tricky, you need to get IP address which is trying to create problem for your server and once you have manage to get such IP you can easily ban such IP from accessing your server. you just have to add this IP in your APF Firewall setting.
*) Login to your server as root
*) Now you need to add IP which is creating problem for your server Within APF Firewall, you simply need to enter apf –d <ip>
*) By default, rebooting server will resets all your IP bans, thus its always recommend to use APF firewall for your dedicated server – with APF, there is an easy workaround. Just open the deny hosts file scroll to the bottom of the file and paste in the IP address you want to ban.
Just save and exit using Ctrl+X then Y, this will save all edited settings as default.
*) Lastly just restart your APF and thats all you have successfully banned the culprit IP which is hammering your server and overloading it.

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